The US said today it would not demand that China commits to binding cuts in its greenhouse gas emissions, marking an important step towards agreement on a global treaty to fight climate change.

The move came at the end of the latest round of UN climate change talks ­involving 183 countries, which aim to produce a deal in Copenhagen in December.

Jonathan Pershing, head of the US ­delegation in Bonn, said developing countries – seeking to grow their economies and alleviate poverty – would instead be asked to commit to other actions. These include increasing energy efficiency standards and improving the take-up of renewable energy, but would not deliver specific reductions.

He said: "We're saying that the actions of developing countries should be binding, not the outcomes of those actions."

Only developed countries, including the US, would be expected to guarantee cuts. The pledge was included in a US blueprint for a climate change deal submitted to the Bonn meeting, which Pershing said was based on the need for rich countries to cut greenhouse gas emissions 80% by 2050. The American plan, if approved, could replace the existing Kyoto protocol. The lack of any carbon targets for ­developing countries in the protocol was the reason the US never ratified it.

While such cuts were believed to be unrealistic in the new treaty, the first clear acceptance of that at the UN talks by the US is being seen as significant. EU officials said they were studying the US proposal.China and the US are the two biggest polluters in the world, making their positions on the deal critical.

In a separate submission to the meeting, China was among a group of developing countries that called on rich countries to cut emissions by 40% by 2020 on 1990 levels. According to the environmental group WWF, commitments made by developing countries so far add up only to about a 10% cut. Japan this week proposed an effective 8% cut in its emissions.

Observers see the 40% demand as unrealistic, suggesting the US move amounts to blinking first in the negotiations. But back-channel negotiations, revealed by the Guardian last month, showed the two countries are searching for a deal.

John Ashe, who chaired discussions at Bonn on how Kyoto targets could be extended, said many of the targets put forward could be revised as the Copenhagen deadline looms. "There is always an initial move and then a final move. I don't believe we're in the final stage yet," he said.

He said China should agree to take actions to control emissions that were measured and reported to the international community.

In Washington, Todd Stern, the state department's climate change envoy, said the US still expected China to move towards a cleaner economy. "We are expecting China to reduce their emissions very considerably compared to where they would otherwise be [with] a business as usual trajectory," he said.

At the end of the talks, the UN's top climate official said progress had been made. Yvo de Boer, executive secretary of the UN framework convention on climate change, said: "A big achievement of this meeting is that governments have made it clearer what they want to see in the Copenhagen agreed outcome."

But green campaigners criticised the failure to resolve issues such as an overall target for 2020 emission reductions or concrete proposals on funding for poor countries to deal with global warming.Antonio Hill of Oxfam said: "The countries that created the nightmare are refusing to lift a finger to prevent it becoming a reality. Rich country delegates have spent two weeks talking but have done nothing on the issues that really matter. They may be kidding themselves they are working towards a deal but they are not kidding anyone else."